Device for cooling, drying and granulating strands

ABSTRACT

A device for cooling, drying, and granulating molten strands issuing from nozzles with an outlet channel, the upper end of which is located below the nozzles, a device, generating a current of cooling liquid over the outlet channel, a granulator arranged downstream of the outlet channel and with a dehydrating section that is arranged upstream of the granulator and in which the strands rest on a support provided with orifices for the unrestricted passage of the cooling liquid. The outlet channel in the region following the dehydrating section is provided with inlet nozzles that inject a current of fluid and that are so close together and arranged over such a length in its bottom that the strands are guided with respect to the bottom virtually without friction along the outlet channel in the granulator arranged at its lower end and with a degree of dehydration that enables immediate further processing.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a device for cooling, drying, and granulatingmolten strands issuing from nozzles and made, e.g., from thermoplastics,with an outlet channel, the upper end of which is located below thenozzles, a device, generating a current of cooling liquid over theoutlet channel, a granulator arranged downstream of the outlet channeland with a dehydrating section that is arranged upstream of thegranulator and in which the strands rest on a support provided withorifices for the unrestricted passage of the cooling liquid.

Such a device is known from the DE-PS 33 36 032. In this device thedehydrating section comprises zones of which the first zone in the flowdirection leads to a water outlet and the second zone is pressurizedwith an air current, by means of which water clinging to the strands islargely sucked off. These two zones of the dehydrating section arearranged practically directly upstream of the granulator.

The invention is based on the problem of further improving the knowndevice, described above, with respect to its drying efficiency andsimultaneously giving the device especially good self-threadingproperties.

The invention accomplishes this in that the outlet channel in the regionfollowing the dehydrating section is provided with inlet nozzles thatinject a current of fluid and that are so close together and arrangedover such a length in its bottom that the strands are guided withrespect to the bottom virtually without friction along the outletchannel into the granulator, arranged at its lower end, with a degree ofdehydration that enables immediate further processing.

The result of inserting the region of the inlet nozzles guiding thecurrent of fluid between the dehydrating section and the granulator isthe combination of two effects. On the one hand, the strands are driedto the extent that they are processed by the granulator with a degree ofdehydration that enables immediate further processing, i.e. the granulesthat are produced do not require any subsequent drying process. Thecurrent of fluid provides that the strands are subsequently guidedvirtually without friction over the bottom, a feature that is especiallysignificant due to the lack of water, which, when present, acts to someextent as a lubricant. The virtually frictionless guiding of the strandsin the region of the inlet nozzles provides that the strands, pushedforward by gravity or the current of cooling liquid, automaticallyobtain a tendency to self-thread, which is otherwise decreased in thearea upstream of the granulator when cooling liquid is lacking.

The tendency for self-threading can be further intensified by slopingthe inlet nozzles in the direction of motion of the strands.

Preferably a current of gas, in particular a current of air, is used forthe current of fluid. It is also possible to use an inert gas, inparticular nitrogen, which is frequently produced in chemical operationsas a side product.

To be able to process especially moisture-sensitive substances, apowdery drying agent is added in an advantageous manner to the currentof gas. Usually such a drying agent also has the effect of preventingthe strands from sticking together. If such a drying agent is undesiredfor the further processing of the granules since said drying agentadheres to the manufactured granules, the outlet channel between thegranulator and the region of the inlet nozzles guiding the current offluid can be provided with perforations leading to a suction chute. Thena current of air sucked in through the suction chute and theperforations removes the powdery drying agent from the strands so thatthe strands are conveyed virtually without any drying agent into thegranulator.

To increase the feed effect of the sloped inlet nozzles, feed nozzlesfor blowing a current of fluid against the strands in the direction ofmovement of the strands can be provided in an advantageous manner in theregion of the inlet nozzles above the outlet channel. Preferably thesame medium is used for this current of fluid as for the current offluid directed through the inlet nozzles. These additional feed nozzlesalso increase the tendency towards self-threading. This is especiallyadvantageous if the inlet nozzles provided in the bottom of the outletchannel pass vertically through the bottom.

To adapt the device to different drying and cooling needs, the region ofthe inlet nozzles guiding the current of fluid and/or the regionupstream of the dehydrating section is/are lengthwise adjustable. Tothis end, a telescopic construction of the regions in question isespecially suitable. In this manner it is possible to combine anespecially long section guiding the current of cooling liquid with ashortened length of the region with the inlet nozzles for the current offluid.

To obtain special drying, cooling or heating effects, the current(s) offluid can be suitably moderated. Thus, for example, it is desirable toheat fiber-reinforced plastic strands by means of the current of fluidin order to thus remove the load from the granulator. Vice versa it isadvantageous for granulating flexible strands to cool them prior togranulating, since in this case better granules are obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show embodiments of the invention.

FIG. 1 is a side view of a principle presentation of the device withsloped outlet channel.

FIG. 2 shows the device with horizontal, lengthwise adjustable outletchannel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The device shown in FIG. 1 has a frame 1, on which the water tank 2 isattached, to which water is fed in known manner and serves here as thecooling liquid. The cooling liquid flows out of the slot nozzle 3 ontothe outlet table 4 and over it to the right as a film of water, whichcarries along with it strands 26 which appear on the outlet table 4 andare made of an extrudable material, in this case thermoplastic. Nozzleset 5, of which one nozzle 6 is shown, is arranged above the outlettable 4. Thermoplastic in the molten state is fed to the set of nozzles5 and forced out of nozzle 6. The design of such a set of nozzles isknown. In the case of the device shown in FIG. 1, several nozzles 6 liecorrespondingly side by side on a line.

Strands 26 issuing from nozzles 6 fall first on the outlet table 4 andare carried along by the film of water flowing over the outlet table 4until said strands arrive by means of end 7 of the outlet table 4 at theoutlet channel 8, on which they slide down in somewhat parallelarrangement. The outlet channel 8 is held in housing 9, which is bracedwith its left side by means of arm 10 on frame 1. Housing 9 has sixcooling water spray nozzles 11, which, if necessary, spray additionalcooling liquid, thus in particular water, on the outlet channel 8 andthus increase the cooling effect exerted on the plastic strands. Theoutlet channel 8 leads with its bottom end the plastic strands 26sliding off over said outlet channel to granulator 13, which comprisesthe two feed rolls 14 and 15 and the rotor 16. Rotor 16 works againstthe stationary knife 17 serving simultaneously as the feed table. Thisconstruction of a granulator is well-known. Granulator 13 is mounted onstands 18.

The outlet channel 8 is provided in front of its bottom end 12 withinlet nozzles that are close to one another and inject a current offluid, shown by arrow 31. This current of fluid is guided through chute32 into tank 33, which is located below the region of the outlet channel8 with inlet nozzles 30. Here an air current, which flows around theplastic strands 26, guided over this region of the outlet channel 8, andlifts off in such a manner from the bottom of the outlet channel 8 thatthe plastic strands 26 are guided virtually without friction, is used asthe current of fluid. To this end the inlet nozzles 30 are provided incorresponding density.

The dehydrating section 19, beneath which the water outlet 21 isarranged, is provided between the region of the outlet channel 8 withthe coolant spray nozzles 11 and the region with the inlet nozzles 30.The dehydrating section 19 comprises a screen, which forms here thebottom of the outlet channel 8. The cooling water supplied at the upperend to the outlet channel 8 drains largely through this screen in theregion of the dehydrating section 19.

The region of the outlet channel 8 with the inlet nozzles 30 receives inthis manner cooled plastic strands 26, which are largely freed of thecooling water. The residual water is removed to some degree from theplastic strands 26 by means of the current of air guided by the inletnozzles 30, so that due to the length of the region with the inletnozzles 30 the strands are fed to the granulator 13 with a degree ofdrying that enables immediate further processing. The granules producedby the granulator 13 fall then with this degree of drying out throughthe delivery chute 27 for further processing.

Inlet nozzles 30 are formed here by upwardly tilted slot or pelletizingnozzle, shown by the saw-tooth line drawing in FIG. 1. Such slot nozzlesare known. However, it must be pointed out that inlet nozzles passingalso vertically through the bottom of the outlet channel 8 can be usedthat, of course, do not give the current of air guided by said nozzlesthe tendency to act on the plastic strands 26 being led down. Such anadditional conveying action can be obtained through the arrangement offeed nozzles 22 which are arranged above the inlet nozzles 30 and whichaim a current of fluid, here also a current of air, tilted downwards atthe plastic strands 26 being led down.

The device shown in FIG. 1 has a pronounced tendency for self-threading,a feature that is significant when starting the device and also in thecase of the plastic strands possibly fracturing or tearing away. Sincein the region of the inlet nozzles 30 the plastic strands are guidedvirtually without friction along the outlet channel 8, the subsequentpushing of the plastic strands 26 due to the feed effect of the coolingwater automatically provides that the plastic strands are conveyedwithout any restrictions into the granulator 13. This tendency ofself-threading is further reinforced by suitable inlet nozzles 30 andalso by the feed nozzles 22.

The embodiment shown in FIG. 2 is a variation of the device according toFIG. 1. The device is provided with a horizontal outlet channel 8.Despite this horizontal direction of the outlet channel 8 it is possibleto transport with it the plastic strands 26 into the granulator 13 so asto self-thread, since a pronounced feed action is exerted on the plasticstrands 26 by means of the current of cooling water led over the outlettable 4 and by the action of the spray nozzles. Since in the relativelylong region with the inlet nozzles 30 the plastic strands are largelyprevented from rubbing on the bottom of the outlet channel 8 owing tothe current of air flowing through there, the thrust given the plasticstrands 26 in the region behind the outlet table 4 provides that theplastic strands 26 are transported reliably into the granulator 13.

In the device, according to FIG. 2, the dehydrating section (referencenumeral 19 in FIG. 1) is further divided into two zones, namely zone 20for the cooling water to drain and zone 23 through which a current ofair is guided in the direction of the drawn arrow 24. This air currenttakes with it a significant portion of the residual water clinging tothe plastic strands, so that plastic strands that are virtually freed ofwater are conveyed into the region of the outlet channel 8 with theinlet nozzles 30.

Here the outlet channel 8 is lengthwise adjustable both in the regionbehind the outlet table 4 and in the region of the inlet nozzles 30, afeature that is indicated by the telescopic construction of theseregions. These two regions can thus be pushed into one another andpulled out of one another, thus enabling an optimal adjustment to theoperating conditions that are demanded from time to time. Theseoperating conditions depend in particular on the plastic to beprocessed.

To be able to compensate for the lengthwise modification in the outletchannel 8 in the region of the granulator 13, granulator 13 is arrangedon the car 25, which rides along by a corresponding length in accordancewith the extension or reduction of the outlet channel 8.

In the device shown in FIG. 2 a suction chute 28, which acts analogouslyto the suction in region 23, is arranged directly upstream of thegranulator 13 at the bottom of outlet channel 8. Correspondingly thebottom of outlet channel 8 is designed here as a screen. Suction takesplace in the direction of the drawn arrow. The arrangement of thissuction chute 28 is logical if a powdery drying agent, e.g., talcum,that is to be removed prior to granulation, is added to the current ofair supplied by the inlet nozzles 30. In this manner the drying agentcan then unfold its effect in the region of the inlet nozzles 30. To theextent it still adheres to the strands 26, it is virtually removed bymeans of the suction chute 28.

We claim:
 1. A device for cooling, drying, and granulating moltenstrands issuing from nozzles, said device comprising an outlet channelhaving an upstream end, a downstream end and a bottom extending fromsaid upstream end to said downstream end, the upstream end of which islocated below the nozzles, means for generating a current of coolingliquid over the outlet channel, and a granulator arranged downstream ofthe outlet channel, said channel including a dehydrating section that isarranged upstream of the granulator and in which the strands rest on asupport provided with orifices for providing unrestricted passage of thecooling liquid, the outlet channel further including a region followingthe dehydrating section, said region being provided with inlet nozzlesthat inject a current of fluid upward through said outlet channel, saidinlet nozzles being so close together and arranged over such a length insaid bottom of said outlet channel so that the strands are guided withrespect to the bottom virtually without friction along the outletchannel and into the granulator with a degree of dehydration thatenables immediate further processing.
 2. A device as claimed in claim 1,wherein the inlet nozzles are sloped so as to point at least partiallyin a direction generally toward said downstream end of said channel. 3.A device as claimed in claim 1, wherein the current of fluid injected bysaid inlet nozzles is a current of gas.
 4. A device as claimed in claim3, wherein said inlet nozzles further inject a powdery drying agent withthe injected current of gas.
 5. A device as claimed in claim 1, whereinthe outlet channel between the granulator and the region of the inletnozzles is provided with perforations leading to a suction chute.
 6. Adevice as claimed in claim 1, further including feed nozzles for blowinga second current of fluid against the strands in a general directiontoward said downstream end of said channel, said feed nozzles areprovided in the region of the inlet nozzles above the outlet channel. 7.A device as claimed in claim 1, wherein at least one of the region ofthe inlet nozzles and the region upstream of the dehydrating section islengthwise adjustable.
 8. A device for cooling, drying, and granulatingmolten strands issuing from nozzles, said device comprising:a channelhaving an upstream end and a downstream end, said channel defining abottom for receiving the strands for movement from said upstream end tosaid downstream end, said channel further defining a cooling section, aninitial drying section and a final drying section, said bottom of saidchannel in said cooling section being substantially imperforate forsupporting a cooling liquid, said bottom of said channel in said initialdrying section having a perforate construction through which saidcooling liquid is substantially removed from said channel, and saidbottom of said channel in said final drying section having openingsthrough which a drying fluid is passed; means for supplying the coolingliquid to said cooling section of said channel to cool the moltenstrands; means for passing the drying fluid upward through said openingsin said bottom of said channel in said final drying section so that saidstrands are further dried and so that said strands are passed along saidchannel toward said downstream end of said channel without incurringsignificant frictional resistance with respect to the bottom of saidchannel; and a granulator adjacent said downstream end of said channelfor granulating said strands.
 9. A device as claimed in claim 8, whereinsaid means for passing said drying fluid into said final drying sectioninjects the drying fluid in a direction inclined generally toward saiddownstream end of said channel.
 10. A device as claimed in claim 8,wherein said openings through which said drying fluid is passed includesa series of openings defined along a length of said bottom of saidchannel in said final drying section.
 11. A device as claimed in claim8, further including means for supplying a powdery drying agent intosaid drying fluid passed through said openings in said bottom of saidchannel in said final drying section.
 12. A device as claimed in claim11, further including a suction chute located before said granulator andmeans for applying a suction through said suction chute so that saidpowdery drying agent is substantially removed from the strands.
 13. Adevice as claimed in claim 8, wherein at least one of said coolingsection and said final drying section of said channel has an extendiblelength.
 14. A device as claimed in claim 8, further including aplurality of fluid nozzles located above said bottom of said channel insaid final drying section, said fluid nozzles being constructed so thateach directs a flow of drying fluid in a direction generally toward saiddownstream end of said channel.
 15. A device as claimed in claim 8,further including means for suctioning a fluid from said initial dryingsection of said channel in a direction generally transverse to saidbottom of said channel to further aid in removing the cooling liquidfrom said channel.
 16. A device as claimed in claim 8, further includingmeans for applying a suction in said initial drying section of saidchannel in a direction generally perpendicular to said bottom of saidchannel, said device further including a pair of chutes located beneathsaid perforate bottom construction of said channel, one of said chutesbeing located upstream relative to the other chute to receive and removesaid cooling liquid from said channel, the other chute being positionedadjacent thereto for applying suction in said initial drying section.17. A device for cooling, drying, and granulating molten strands issuingfrom nozzles, said device comprising:a channel having an upstream endand a downstream end, said channel further defining a bottom forreceiving the strands for movement therealong from said upstream end tosaid downstream end; means for generating a current of cooling liquidover said channel adjacent said upstream end; means for removing thecooling liquid in said channel; means for injecting a drying fluidupward from said bottom of said channel adjacent said downstream end sothat said strands move toward said downstream end without incurringsignificant frictional resistance with respect to said bottom of saidchannel; and a granulator adjacent said downstream end of said channelfor granulating the strands passed thereto through said channel.
 18. Adevice as claimed in claim 17, further including means for applying asuction in said bottom of said channel near said means for removing saidcooling liquid to effect at least partial drying of the strands.
 19. Adevice as claimed in claim 17, further including means for supplying apowdery drying agent into said drying fluid injected upward from saidbottom of said channel.
 20. A device as claimed in claim 19, furtherincluding means for removing the powdery drying agent from the strands.